This application claims the priority of German Patent Application Serial No. 100 31 610.7, filed Jun. 29, 2000, the subject matter of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates, in general, to a chain tensioner, and more particularly to a chain tensioner as used in chain drives of internal combustion engines.
2. Description of Prior Art
European Pat. No. 0 195 945 B1 describes a chain tensioner which includes a housing and a spring-biased piston received in the housing for axial displacement against a chain. Before installation of the chain tensioner, the piston is fixed in place within the housing by a transport safety mechanism. The housing is provided with boreholes for receiving screw fasteners to secure the housing to a stationary machine element. After attachment of the housing to the stationary machine element, the transport safety mechanism is removed, so that the piston can move under the action of the spring against the confronting strand of the chain.
The piston should have a sufficient operating stroke to keep the chain under tension. In addition, the operating stroke must be so sized as to reliably compensate for tolerances that are normally encountered in chain drive systems. In the event the distances of the center axes of the sprockets are smaller than the desired size, but still within the admissible tolerance range, the chain strand to be tensioned may undergo in the plane as covered by the chain greater deflections that have to be absorbed by the operating stroke of the chain tensioner. As a consequence of the greater operating stroke, the chain tensioner must be built of greater size, thereby increasing manufacturing costs and requiring a greater installation space. In view of the very compact structure of current internal combustion engines for motor vehicles and the available limited space for auxiliary aggregates, the chain tensioners according to European Pat. No. 0 195 945 B1 is unable to reconcile the contradicting demands, namely to ensure a sufficient operating stroke, on the one hand, and to provide a smallest possible chain tensioner.
It would therefore be desirable and advantageous to provide an improved chain tensioner to obviate prior art shortcomings.
According to one aspect of the present invention, a chain tensioner, includes a housing intended for attachment to a stationary machine element of an internal combustion engine, a piston received in the housing for axial displacement against a strand of a chain to thereby implement a tensioning of the chain; an adjusting mechanism for moving the housing relative to the machine element in a direction to and away from the strand of the chain; and a spacer for establishing a distance between the housing and the strand to thereby define a proper installation position of the housing.
Through the provision of a chain tensioner according to the present invention, the intended operating stroke of the piston can be dimensioned independently of tolerances of the chain drive. In situations, when the chain has great dimensions and thus covers a wide plane so that the chain strand being tensioned may be deflected to a substantial extentxe2x80x94because the smallest possible distance of the center axes of the sprockets is definedxe2x80x94the housing of the chain tensioner is moved in the direction of the chain strand being tensioned until the spacer abuts against the chain strand or against a tensioner bar that bears upon the chain strand. Optionally, the housing can then be moved even further until the chain strand reaches its maximum deflection. This defines the installation position of the housing, which can then be secured to the machine element. The spacer is hereby dimensioned for the type of chain drive being used.
Unlike in conventional chain tensioner, the piston of the chain tensioner according to the present invention is not intended to compensate for chain drive tolerances. As soon as the housing is displaced transversely to the chain strand and shifted at an oblique angle with respect to the chain strand, a displacement is effected in adjusting direction.
According to another feature of the present invention, the adjusting mechanism may be implemented in a simple manner by openings, in particular oblong holes, formed in the housing for receiving fasteners, such as screw fasteners, which are threadably engageable in the stationary machine element. As the housing of chain tensioners is typically mounted to the engine block or cylinder head by machine screws, and the housing has oblong holes at the adjusting directions, the adjusting mechanism can be realized without requiring additional parts.
The spacer may be supported by the housing and include a stop member for abutment against the chain strand or against a tensioner bar bearing against the chain strand. Attachment of the spacer and the stop member to the chain tensioner may be carried out already before installation of the chain tensioner depending on the intended chain drive. After securement of the housing of the chain tensioner, the spacer can be moved away from the tensioner bar or from the chain strand. The spacer may be articulated to the housing and simply be swung out, once the housing occupies the proper installation position. Of course, the spacer may also be so configured as to be completely removable after installation of the chain tensioner. It is also conceivable, to configure the spacer as a template for use by the installer during installation of the chain tensioner. After concluding the installation, the template may be removed again.
According to another feature of the present invention, the chain tensioner may also be combined with a detachable transport safety mechanism for holding the piston in transport position, i.e. locks the piston in place during transit or storage of the chain tensioner. Suitable, the spacer forms hereby part of the transport safety mechanism. For example, the transport safety mechanism may include a retainer arm which forms the spacer and embraces an end portion of the piston. The extension of the retainer arm between the piston and the chain strand or the tensioner bar bearing upon the chain strand is hereby so dimensioned that the installation position of the housing can be established in a manner as described above.
Installation and activation of a chain tensioner according to the present invention is simple. When the chain tensioner includes an internal locking mechanism for captivating the piston within the housing, the spacer may be designed as a component separated from the transport safety mechanism. In this case, the housing is shifted in adjusting direction toward the chain strand until the predetermined installation position has been implemented. Then, the housing is securely fixed to the machine element. Finally, the spacer is moved out of contact with the chain strand or the tensioner bar.
In the event, the chain tensioner is provided with a separate transport safety mechanism with integrated spacer, the housing is also securely fixed in the predetermined installation position. Subsequently, the transport safety mechanism is loosened and, optionally, removed, to move the spacer out of contact from the chain strand or tensioner bar. After loosening or removing the transport safety mechanism, the piston can move against the chain strand or tensioner bar.